A reflecting optic telescope is widely applied in an astronomical telescope. Since the reflecting optic system does not have special requirement on the optic property of glass materials, and the light does not need to penetrate through the materials, light weight processing may be conducted on the main telescope to reduce the weight without a chromatic aberration; moreover, an optic material of the large-aperture lens is rare, and is expensive. Therefore, a reflecting structure design is usually used in the large-aperture telescope. The light path of the large-aperture reflecting telescope is generally in an open structure. When the large-aperture reflecting telescope is used in an extremely low temperature environment, a phenomenon of frosting on the telescope mirror surface may occur, which leads to the failure of normal observation.
A transparent conducting film layer (ITO) is widely used in an LCD, a touch screen and a solar energy element. The transparent conducting film is a heavy-doped n-type semiconductor with high degeneracy, and has lower specific resistance which is about 10−4 Ω·cm, and a forbidden bandwidth is between 3.5 eV and 4.5 eV. Therefore, the absorption in a visible region is very little, and the average penetration rate after plating may reach to more than 85%. The transparency and the electrical conductivity of a substance are preferably unified by the electric conductivity close to metal and the high penetration rate in the visible light scope of the transparent conducting film layer.
The transparent conducting film is widely used in a solar cell, a display, a gas sensitive element, an antistatic coating, windows of modern warplanes and cruise missiles, an infrared radiation reflector coating, gloss defrosting used in planes and trains, wall glass of buildings and other aspects by the electric conductivity close to metal, the high penetration rate and the high infrared reflecting rate in the visible light scope, and the semiconductor property thereof.
The existing optic reflecting reflectors in the optic plating technology include a metal reflector and an all-dielectric reflector. The most common metal materials used in the metal reflector comprise aluminum (AL), argentum (Ag), gold (Au), etc. A single layer or multi-layer dielectric film is provided on the reflecting film, which protects the metal film and increases the reflection of a specific band. The all-dielectric reflector is composed of dielectric film pack materials with alternatively high and low refractive indexes. When an ordinary metal reflector or an all-dielectric reflector is used in the optic telescope with the large-aperture reflecting open structure, the difficulty of failure on observation caused by frosting on the telescope mirror surface may occur under the antarctic environment with an extremely low temperature.
At present, all the antarctic astronomical telescopes are designed with a small-aperture penetration-type sealed structure, and a window sealing glass plated with a transparent conducting film is used in the front surface of the telescope to achieve the frost-prevention function of the telescope. The transparent area of the transparent conducting film is in a visible light and near-infrared band, while strong absorption appears in an infrared band. Therefore, this structure design is not suitable for a large-aperture reflecting optic infrared telescope, as shown in FIG. 3.